Styrene cobalt catalysts

Two molecules of carbon monoxide were successively incorporated into an epoxide in the presence of a cobalt catalyst and a phase transfer agent [29]. When styrene oxide was treated with carbon monoxide (0.1 MPa), excess methyl iodide, NaOH (0.50 M), and catalytic amounts of Co2(CO)8 and hexadecyltrimethylammonium bromide in benzene, 3-hydroxy-4-phenyl-2(5H)-furanone was produced in 65% yield (Scheme 7). A possible reaction mechanism was proposed as shown in Scheme 8 Addition of an in situ... 

Lu and coworkers have synthesized a related bifunctional cobalt(lll) salen catalyst similar to that seen in Fig. 11 that contains an attached quaternary ammonium salt (Fig. 13) [36]. This catalyst was found to be very effective at copolymerizing propylene oxide and CO2. For example, in a reaction carried out at 90°C and 2.5 MPa pressure, a high molecular weight poly(propylene carbonate) = 59,000 and PDI = 1.22) was obtained with only 6% propylene carbonate byproduct. For a polymerization process performed under these reaction conditions for 0.5 h, a TOF (turnover frequency) of 5,160 h was reported. For comparative purposes, the best TOF observed for a binary catalyst system of (salen)CoX (where X is 2,4-dinitrophenolate) onium salt or base for the copolymerization of propylene oxide and CO2 at 25°C was 400-500 h for a process performed at 1.5 MPa pressure [21, 37]. On the other hand, employing catalysts of the type shown in Fig. 12, TOFs as high as 13,000 h with >99% selectivity for copolymers withMn 170,000 were obtained at 75°C and 2.0 MPa pressure [35]. The cobalt catalyst in Fig. 13 has also been shown to be effective for selective copolymer formation from styrene oxide and carbon dioxide [38]. 

Cobalt catalysts have been shown to hydrogenate arenes to saturated hydrocarbons. The Co(acac)2-AlHBu 2-PBun3 system hydrogenates benzene to cyclohexene, but the presence of styrene was necessary, otherwise the reaction ceased. The styrene was also hydrogenated.72... 

Although cobalt catalysts have been rarely used in cyclopropanation reactions, Nakamura and coworkers2 1 have developed the camphor-based complex (35) as a useful asymmetric catalyst, as shown in a typical example in equation (16). High yields were obtained with dienes and styrenes but cyclopropanation did not occur with simple alkenes. Studies with cu-ife-styrene showed that, unlike other catalytic systems, the reaction was not stereospecific with respect to alkene geometry. 

The only substrate which has been hydroformylated using chiral cobalt catalysts with an optical yield comparable to those obtained with other metals is styrene (Table 1) in fact, in this case, optical yields up to 15% were obtained working in the presence of ethyl orthoformate15) to avoid racemization of 2-phenylpropanal. The changes in the prevailing absolute configuration of the synthesized aldehyde observed both in the styrene and 2-phenyl-1-propene hydroformylation upon... 

Health hazards (mostly allergens) observed with UP composites are usually either due to non-crosslinked UP, mainly due to remnants as mentioned previously (such as, styrene, cobalt naphthanate, phthalates or tricresyl phosphate, benzoyl peroxide and other catalysts) or to the under-cured resin (i.e., UP automobile repair putty). Benzoyl peroxide is known to be a strong skin irritant [70]. 

A heterogeneous cobalt catalyst was employed for arylations of styrene (2) and two acrylates with aryl iodides. Generally, isolated yields were significantly lower than those observed for heterogeneous nickel catalysts [24]. Further, a silica-supported poly-y-aminopropylsilane cobalt(II) complex was reported as a highly active and stereoselective catalyst for Mizoroki-Heck-type reactions of styrene (2) and acrylic acid (16) using aryl iodides [23,25]. 

A remarkable acceleration effect on the ring-opening of various epoxides with HCo(CO)4 was achieved by the addition of small amounts of Lewis bases such as alcohols (ethanol, butanol) [8]. In this maimer, the hydroformylation of propylene oxide was accelerated by a factor of 100. An improvement of conversion was also observed in the presence of acetone, diethyl ether, or THE (tetrahydrofu-ran). Low reaction temperatures stimulated hkewise the selective formation of hydroxy aldehydes. With styrene, mainly isomeric diols were obtained because of the high reducing power of the cobalt catalyst. Epichlorohydrin yielded mainly ethyl y-chloro-P-hydroxypropionate. The relative reactivity of the olefin oxides toward these hydroformylation conditions was found to be in the following order (Figure 6.15). 

Weiser and Mulhaupt reported that cobalt(ll) ortanoate (Co-8) and perfluorooctanoate (Co-9) catalyzed the normal atom transfer polymerization in the presence of the bromide initiator under homogeneous and fluorous biphasic conditions. The cobalt(ll) perfluorooctanoate, which was prepared in situ from C0CI2 and sodium salts, and 1-phenylethylbromide produced polystyrene (Mn<2500) with relatively narrow MWDs (Mw/Mn<1.5) at 90 °C. Temperature-induced lower critical solution temperature (LCST) phase separation occurred at room temperature for the effective separation of the perfluorinated catalyst from the products. Furthermore, both the cobalt catalysts and fluorous media were recyclable without any loss in the catalytic activity. A simple cobalt(II) acetate (Co-10) could also induce the controlled polymerization of MMA and styrene. Using cobalt acetate as a catalyst and tosyl chloride as an initiator, the polymerization of MMA took place without additives in DMF at 60 °C, in which the M of the obtained polymer linearly inaeased with the conversion along with narrow MWDs (Mw/M = 1.26). The bulk polymerization of styrene was also successfully catalyzed by cobalt acetate and the obtained... 

Catalyst Selection. The low resin viscosity and ambient temperature cure systems developed from peroxides have faciUtated the expansion of polyester resins on a commercial scale, using relatively simple fabrication techniques in open molds at ambient temperatures. The dominant catalyst systems used for ambient fabrication processes are based on metal (redox) promoters used in combination with hydroperoxides and peroxides commonly found in commercial MEKP and related perketones (13). Promoters such as styrene-soluble cobalt octoate undergo controlled reduction—oxidation (redox) reactions with MEKP that generate peroxy free radicals to initiate a controlled cross-linking reaction. 

Cyclopropanation of C=C bonds by carbenoids derived from diazoesters usually occurs stereospeciflcally with respect to the configuration of the olefin. This has been confirmed for cyclopropanation with copper 2S,S7,60 85), palladium 86), and rhodium catalysts S9,87>. However, cyclopropanation of c -D2-styrene with ethyl diazoacetate in the presence of a (l,2-dioximato)cobalt(II) complex occurs with considerable geometrical isomerization88). Furthermore, CuCl-catalyzed cyclopropanation of cis-2-butene with co-diazoacetophenone gives a mixture of the cis- and trans-1,2-dimethylcyclopropanes 89). 

Enantioselective carbenoid cyclopropanation can be expected to occur when either an olefin bearing a chiral substituent, or such a diazo compound or a chiral catalyst is present. Only the latter alternative has been widely applied in practice. All efficient chiral catalysts which are known at present are copper or cobalt(II) chelates, whereas palladium complexes 86) proved to be uneflective. The carbenoid reactions between alkyl diazoacetates and styrene or 1,1 -diphenylethylene (Scheme 27) are usually chosen to test the efficiency of a chiral catalyst. As will be seen in the following, the extent to which optical induction is brought about by enantioselection either at a prochiral olefin or at a prochiral carbenoid center, varies widely with the chiral catalyst used. 

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